Leetcode 257. Binary Tree Paths

文章作者：Tyan
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1. Description

Binary Tree Paths

2. Solution

• Recursive

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<string> binaryTreePaths(TreeNode* root) {
        vector<string>  result;
        if(root == NULL) {
            return result;
        }
        searchPath(root, "", result);
        return result;
    }
    
    void searchPath(TreeNode* root, string s, vector<string>& result) {
        if(s == "") {
            s = to_string(root->val);
        }
        else {
            s = s + "->" + to_string(root->val);
        }
        if(root->left == NULL && root->right == NULL) {
            result.push_back(s);
            return;
        }
        if(root->left != NULL) {
            searchPath(root->left, s, result);
        }
        if(root->right != NULL) {
            searchPath(root->right, s, result);
        }
    }
};

• Iterative

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<string> binaryTreePaths(TreeNode* root) {
        vector<string>  result;
        if(root == NULL) {
            return result;
        }
        queue<TreeNode*> nodes;
        queue<string> paths;
        nodes.push(root);
        paths.push("");
        while(!nodes.empty()) {
            TreeNode* node = nodes.front();
            nodes.pop();
            string path = paths.front();
            paths.pop();
            if(path == "") {
                path = to_string(node->val);
            }
            else {
                path = path + "->" + to_string(node->val);
            }
            if(node->left == NULL && node->right == NULL) {
                result.push_back(path);
                continue;
            }
            if(node->left != NULL) {
                nodes.push(node->left);
                paths.push(path);
            }
            if(node->right != NULL) {
                nodes.push(node->right);
                paths.push(path);
            }
        }
        return result;
    }
};

Reference

1. https://leetcode.com/problems/binary-tree-paths/description/